1. Field of the Invention
This invention relates to an image read-out device, and more particularly to a device for reading out an image recorded in a stimulable phosphor by impinging stimulating rays upon the stimulable phosphor and measuring the light emitted by stimulation.
2. Description of the Prior Art
When a stimulable phosphor is exposed to radiations like X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays and ultraviolet rays, a part of the energy of the radiation is stored in the stimulable phosphor. Then, when the stimulable phosphor stored with the radiation energy is exposed to stimulating rays, the phosphor emits light. The amount of the emitted light depends upon the amount of the energy stored.
By utilizing the stimulability of the stimulable phosphor, it is possible to once record an X-ray image of a human body or the like on a sheet like stimulable phosphor plate and read out the recorded image by scanning the plate with a laser beam or the like which stimulates the phosphor and measuring the emitted light with a photosensor. In the prior art, it is known to provide an X-ray image producing apparatus which utilizes the stimulability of a stimulable phosphor as mentioned above to record on a photographic film the X-ray image by modulating a recording light beam scanning the film with the image information obtained by the photosensor which measures the amount of light emitted by the stimulable phosphor as disclosed, for instance, in U.S. Pat. No. 3,859,527.
In the above described apparatus, stimulating rays impinging upon the stimulable phosphor comes at right angle and the emitted light from the phosphor goes back along the optical axis of the stimulating rays, and a large semi-transparent mirror is located apart from a stimulable phosphor inclined at 45.degree. with respect to the optical axis. Stimulating rays impinge upon the stimulable phosphor transmitting through the semi-transparent mirror. The light emitted by the stimulable phosphor by stimulation is reflected by the semi-transparent mirror and converged by a condenser lens and input into a photosensor.
The light emitted by the stimulable phosphor has no directivity and has small intensity. Therefore, the light collecting or converging efficiency must be maximized by enlarging the light receiving solid angle. When the light collecting efficiency is small, the S/N ratio is lowered and there is a possibility that the signal cannot be detected at all.
In the above described apparatus of the prior art, the light receiving solid angle cannot be sufficiently enlarged due to the structure of the apparatus and the light collecting efficiency is low.